In order to facilitate voice communication within Long Term Evolution (LTE) networks, various proposals have been forthcoming of which one comprises so-called CS fallback in which a LTE User Equipment (UE) is arranged to “fallback” to, for example, GSM or UMTS, for the receipt/transmission of incoming/outgoing voice communication.
CS fallback within EPS is primarily realised by using the SGs interface mechanism provided between a Mobile Switching Centre (MSC) server/Visitor Location Register (VLR) or a Mobile Switching Centre (MSC)/Visitor Location Register (VLR) and the Mobility Management Entity (MME).
The SGs interface functionality is derived from the mechanisms specified for the Gs interface in accordance with 3GPP TS 23.060.
Further, from 3GPP TS 23.272 there is provided an arrangement for transporting SMS messages between a UE operating within a E-UTRAN (Evolved UMTS Terrestrial Radio Access Network) and the MSC within a CS domain, by way of the SGs interface between the MME and the MSC/VLR for UEs attached to both EPS services and non-EPS services (CS services).